You missed one very important line: > library(Matrix)
This is not R, it is package Matrix, and the error is in that package, as traceback() shows: > traceback() 6: sprintf(gettext(fmt, domain = domain), ...) 5: gettextf("not-yet-implemented method for %s(<%s>, <%s>).\n ->> Ask the package authors to implement the missing feature.", fun, cl1, cl2) 4: stop(gettextf("not-yet-implemented method for %s(<%s>, <%s>).\n ->> Ask the package authors to implement the missing feature.", fun, cl1, cl2), call. = FALSE) 3: .bail.out.2("solve", class(a), class(b)) 2: solve(XtXu) 1: solve(XtXu) I also suggest you find out about crossprod(). You don't need package Matrix to do this, and squaring a matrix (XtX) to form XtX inverse is not good practice. (Hint: what are the calculations used to find the variance-covariance matrix in a regression? You are effectively doing a Cholesky decomposition of XtX, and how does that relate to decompositions of X, e.g. QR and SVD?) On Wed, 3 Oct 2007, kevinchang wrote: > > Hi all, > > > I am using R trying to get a inverse matrix of (X^T)X , but I keep getting > the error > message like: no b argument and no default value for sprintf(gettext(fmt, > domain = domain), ...) . > -------------------------------------------------------------------------------------------- > # my code > > X<-Matrix(rep(1,500),100,5) > X[lower.tri(X)]<-1-10^-7 > XtX<- t(X)%*% X > XtXu<-lu(XtX) > InverseXtX<-solve(XtXu) > > --------------------------------------------------------------------------------------------- > > The cause suggested for this error is that the lower.tri function returns a > matrix of logicals. If so, is trying to fix this by using sprintf function a > good idea ? Or is there is any alternative way to get the inverse matrix? > Please help. Thanks > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.